On a sunny summer day in July 2013, a 5-year-old boy and his family visited relatives in St. Bernard Parish, Louisiana. The last thing on their mind was a brain-eating amoeba. The boy played outside for much of the day on a slip 'n slide, as kids do. All was well until nine days later, when he started to vomit and complained of an excruciating headache. He developed a high fever: 104 degrees. Tylenol didn’t help.
The symptoms were concerning, but still could have passed for a bad case of the flu. But then the boy had two brief “staring episodes,” where for a few seconds each he gazed straight ahead, unresponsive.
His family took him to a New Orleans hospital, where his condition worsened. The doctors suspected meningitis, a swelling of the membranes surrounding the brain, which can be caused by infection of viruses or microorganisms like bacteria, and he was put on several antibiotics. They performed a CT scan, a spinal tap and other tests to try and narrow down the particular type of infection, but got no clear answer. Several days later he suffered seizures and doctors performed emergency brain surgery. But the infection—whatever it was—and the inflammatory immune response was just too much. He was declared brain dead and the family agreed to cut off life support, five days after the boy was first admitted.
Tests by the Centers for Disease Control and Prevention (CDC) soon suggested that the culprit was Naegleria fowleri, also known as the “brain-eating amoeba.” It has earned that moniker for a good reason, since it can effectively digest neural tissues, says Jennifer Cope, a medical epidemiologist for the CDC in Atlanta.
While the microorganism is normally harmless and found in warm freshwater lakes throughout the South, it can infect the brain if it gets far up into the nasal passages. Once there, it passes through a porous bone separating the sinuses and the brain and begins to break down nerve cells. This triggers brain-swelling, and the resulting syndrome, called primary amebic meningoencephalitis (PAM), is nearly always fatal. Luckily, it’s always very rare, killing between zero and eight people each year in the United States.
In a study published this month in the journal Clinical Infectious Diseases, researchers from the CDC and elsewhere confirmed the boy died of PAM and described the case in full. This is the first confirmed instance in which somebody acquired the deadly infection from tap water, says Cope, a study author.
In the majority of cases, the amoeba is acquired when people swim in warm lakes in the summer and get water up their nose. Victims tend to be disproportionately male and young, with a median age of 12. But in the past few years, new routes of transmission are popping up, including this instance.
Two years before this case, two people who also happened to live in Louisiana died of PAM after using neti pots, which are used to flush the sinuses with salty water. One of these cases also occurred in St. Bernard Parish, and researchers suspect it may be due in part to the fact that Hurricane Katrina inflicted lasting damage to the water system, making it more prone to leaks and contact with soil (where these amoebae can also be found). But they can’t say for certain that the storm was to blame—no water system is a completely “closed loop,” and microorganisms from the environment often find their way into the water, Cope adds.
In 2012, a Muslim man practicing ritual ablution (which includes cleansing the sinuses with water) also came down with the fatal infection in the U.S. Virgin Islands. The CDC generally now recommends using bottle or sterilized water for nasal rinses, though the relative risk of getting PAM from a sinus rinses is very, very small. You are much more likely to get struck by lightning, for example, Cope says.
Water systems use chlorine to kill these microbes, but in this case it appeared that the chlorine levels in the house were low due to evaporation of the water-dissolved gas. Since 2013, Louisiana has started more aggressively chlorinating and testing for N. fowleri, and there hasn’t been a case in the state since then.
The amoeba is on the move, perhaps because temperatures are increasing. Once only found in the South, the microbe and the infection it causes have popped up in Minnesota, Kansas and Indiana. Perhaps strangely, given its spread, the number of cases of PAM don’t appear to be increasing.
Francine Marciano-Cabral, a microbiologist at Virginia Commonwealth University who studies N. fowleri, is investigating how the amoeba becomes infectious. “This is a free-living amoeba that doesn't have to infect anybody, it's perfectly happy feeding on bacteria,” she says. “What we want to find out is why in some people is it so pathogenic and deadly and what makes it that way?” No answers have yet emerged. Perhaps surprisingly, most people that have been tested (albeit in a few small studies in the South) have antibodies against this amoeba, suggesting they’ve been exposed to it at some time in their life, Marciano-Cabral says.
This study will help doctors to be more aware of PAM, despite its rarity, says Marciano-Cabral, who wasn’t involved in the work. In suspected PAM cases the CDC now makes available a drug called miltefosine on an emergency basis, which has some effectiveness against the amoeba. Use of this drug, which isn’t yet commercially available, may have helped cure an Arkansas girl infected with the amoeba in 2013. She is one of only three known American survivors of the affliction.